Influence of high-frequency electromagnetic field-assisted TIG surface modification on microstructural evolution, elemental redistribution and hardness of EN-GJV-400 compacted graphite iron

Introduction. Compacted graphite iron (EN-GJV-400) is widely used for highly loaded automotive and engineering components due to its favourable combination of strength, thermal conductivity, damping capacity and castability. However, the relatively moderate hardness and wear resistance of its surface region may limit its application under severe contact conditions. High-frequency electromagnetic field (HFEMF)-assisted treatment represents a potential approach for modifying solidification conditions and improving structural uniformity during surface engineering. Nevertheless, the influence of HFEMF-assisted TIG treatment on the microstructural evolution, elemental redistribution and hardness response of compacted graphite iron remains insufficiently understood. Materials and methods. In this study, conventional and HFEMF-assisted TIG surface modification of EN-GJV-400 compacted graphite iron was investigated. The experimental program included TIG remelting, TIG surface alloying using Ni78Si8B14 and CuSn-4 foils, and TIG hardfacing using UTP A DUR 600 chromium-containing filler wire, performed with and without electromagnetic assistance. A high-frequency electromagnetic field with a frequency of 200 kHz was applied during treatment. The modified surface layers were characterized using optical microscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM/EDS) and Vickers microhardness measurements. Results and discussion. The obtained results indicate that HFEMF-assisted processing influences the structural development of TIG-modified layers by affecting the conditions of heat and mass transfer during melting and solidification. The influence of HFEMF was evaluated indirectly through surface morphology, microstructural characteristics, elemental distribution and hardness response. Conventional TIG remelting increased the surface hardness of EN-GJV-400 from approximately 375 HV0.1 to 765 HV0.1 due to graphite dissolution, carbon redistribution and formation of ledeburitic structures containing cementite-rich constituents. HFEMF-assisted remelting produced a comparable hardness level of approximately 760 HV0.1, indicating that electromagnetic assistance does not act as an independent strengthening mechanism but mainly contributes to structural homogenization. Ni78BSi8B14 alloying resulted in hardened transformation products together with ledeburitic and carbide-containing constituents, while HFEMF primarily improved the uniformity of alloy-element distribution. For UTP A DUR 600 hardfacing, HFEMF-assisted treatment increased the average hardness from approximately 771 HV0.1 to 800 HV0.1, which is attributed to improved redistribution and more uniform formation of chromium-containing hard phases. Conclusion. The results demonstrate that HFEMF-assisted TIG treatment provides an additional process-control parameter for surface modification of EN-GJV-400 compacted graphite iron. The effectiveness of electromagnetic assistance depends on the chemical composition of the modified layer and the dominant strengthening mechanism. HFEMF should therefore be considered primarily as a method for improving structural uniformity, elemental redistribution and phase distribution rather than as a universal hardness-enhancement technique. Further studies involving direct molten-pool observation and numerical modelling are required to quantitatively establish the relationship between electromagnetic parameters and melt-pool behaviour.